Porous oxygen activated heater

ABSTRACT

An substrate heater includes at least a wet porosity of between 15-35% to allow for sufficient electrolyte solution and porosity for access of a reducing agent within the substrate and oxygen.

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims priority to U.S. Provisional Application No. 61/583,410 filed on Jan. 5, 2012, and to U.S. Provisional Application No. 61/583,418 filed on Jan. 5, 2012, both of which are incorporated herein by reference in their entirety.

FIELD OF THE INVENTION

The invention relates to a porous heater that uses oxygen (generally atmospheric oxygen) as a source of a chemical reactant for an exothermic reaction.

BACKGROUND OF THE INVENTION

Portable flameless heaters are currently used in a variety of applications, such as heating comestible, medical, and consumer items.

Some heaters utilize the reaction of magnesium and water to produce heat. While such a heater produces a sufficient amount of heat, hydrogen gas is product of the exothermic reaction. This can generate safety, transportation, storage, and disposal concerns. In addition, the exothermic reaction requires water, which can be tiresome to constantly carry around.

Other heaters utilize the heat from the reaction of “quicklime” (calcium oxide) and water. While this reaction does not generate hydrogen as a byproduct, it still is based upon using water as a reactant. Accordingly, this type of heater also requires a user to constantly have a sufficient amount of water. Furthermore, the specific energy of the system is low (approximately 1.2 kJ per gram of calcium oxide), making it a suitable, but ineffective, alternative to the magnesium and water heaters.

In addition to the water-based heaters described above, it is known to utilize oxygen-based heaters. Oxygen-based heaters, such as those described in U.S. Pat. Nos. 5,984,995, 5,918,590 and 4,205,957, have certain benefits over water-based heaters.

First, oxygen-based heaters do not require the addition of water to generate heat. Second, because oxygen-based heaters generate heat only in the presence of oxygen, the exothermic reaction can be stopped by simply preventing oxygen access. In addition, some such heaters allow for the exothermic reaction to be restarted at a later time by re-introducing oxygen. Furthermore, since oxygen is abundant in the atmosphere, these heaters do not require mixing of components or additional reactants (as oxygen from the atmosphere is the only missing reactant).

The assignee of the present invention has provided oxygen-base heaters and various packages for same. See, e.g., U.S. Pat. No. 7,722,782, issued on May 25, 2010; U.S. application Ser. No. 12/376,927, filed on Feb. 9, 2009; U.S. application Ser. No. 12/874,338, filed on Sep. 2, 2010; U.S. application Ser. No. 61/583,418, filed on Jan. 5, 2012; U.S. application Ser. No. 61/714,526, filed on Oct. 16, 2012; U.S. application Ser. No. 61/716, 226, filed on Oct. 19, 2012; U.S. application Ser. No. 61/716,279, filed on Oct. 19, 2012; and, U.S. application Ser. No. 61/716,906, filed on Oct. 22, 2012, all of which are incorporated herein by reference.

These disclosed heaters and packages are successful at providing an oxygen based heater and/or package for same.

Since these heaters typically are a porous composite structure and rely on the reaction of atmospheric oxygen with a chemical constituent of the heater composite, the porosity of the composite heater is an important feature for providing an efficient and effective heater.

The present invention is directed to providing a heater that has sufficient porosity so as to be efficient and effective without compromising performance, as well as other benefits.

SUMMARY OF THE INVENTION

In one aspect of the present invention, the present invention is directed towards an oxygen based heater with a wet porosity of approximately 15-35%. The heater may also include a dry porosity of approximately 60%.

In another aspect of the present invention, the present invention is directed towards a heater with the wet porosity of approximately 15-35% in a package.

The dry porosity refers to the porosity of the heater sheet before the electrolyte is introduced, and the wet porosity refers to the porosity of the sheet after electrolyte has been added. The organization of the components within the heater sheet to achieve these porosity ranges is an important attribute to ensure that the heater includes the right micro-environment for the oxygen initiated reaction to occur and these porosity ranges are an indication of establishing the right microstructure.

If the dry or wet porosity is too small, oxygen diffusion to the reaction sites is reduced and, therefore, the heater performance is reduced.

On the other hand, if the dry porosity is too high, the integrity of the heater sheet is compromised and this can impact the ability to manufacture and handle the sheet.

Similarly, if the wet porosity is too high, the performance of the heater sheet will be reduced due to a lack of electrolyte to support the reaction.

Accordingly, the present invention is also directed at providing a heater with a wet porosity sufficient to reach a desired temperature in an acceptable amount of time.

These and other benefits should be apparent to those of ordinary skill in the art in view of the present disclosure.

It is to be understood that the aspects and objects of the present invention described above may be combinable and that other advantages and aspects of the present invention will become apparent to those having ordinary skill in the art upon reading the following description of the drawing and the detailed description thereof.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will become more fully apparent from the following description and appended claims, taken in conjunction with the accompanying drawings. Understanding that the accompanying drawings depict only typical embodiments, and are, therefore, not to be considered to be limiting of the scope of the present disclosure, the embodiments will be described and explained with specificity and detail in reference to the accompanying drawings as provided below.

FIG. 1 is a graph showing the temperature after 5 minutes for various heaters according to the present invention.

FIG. 2 is a graph showing the time it takes various heaters according to the present invention to achieve a 100° F. temperature rise (starting from a 40° F. temperature).

FIG. 3 is a graph showing the time it takes heaters according to the present invention to reach their respective maximum temperatures.

FIG. 4 is a side cutaway view of an embodiment of a heater according to the present invention in a package.

DETAILED DESCRIPTION OF THE DRAWINGS

While this invention is susceptible of embodiment in many different forms, there is shown in the drawings and will herein be described in detail one or more embodiments with the understanding that the present disclosure is to be considered as an exemplification of the principles of the invention and is not intended to limit the invention to the embodiments illustrated.

Reference throughout this description to features, advantages, objects or similar language does not imply that all of the features and advantages that may be realized with the present invention should be or are in any single embodiment of the invention. Rather, language referring to the features and advantages is understood to mean that a specific feature, advantage, or characteristic described in connection with an embodiment is included in at least one embodiment of the present invention. Thus, any discussion of the features and advantages, and similar language, throughout this specification may, but does not necessarily, refer to the same embodiment.

Various composite heaters were prepared by forming sheets of material using a standard mixing and rolling process developed by the and with the formulation shown in Table 1. The heater includes Zn as a reducing agent. The heater also includes carbon treated with KMnO₄ as a promoter and a polytetrafluoroethylene as a binding agent that holds the chemical constituents together and allows for a flexible composite heater to be made. A preferred carbon is Ketjenblack KB300J produced by AkzoNobel Polymer Chemicals, and a preferred polytetrafluoroethylene is a powdered polytetrafluoroethylene such as Laurel Product's Marzon-10. Other chemical constituents could be included and still fall within the scope of the present invention. For example, the heater may also include additives to improve stability such as indium, bismuth, stannates, or silicates.

TABLE 1 Sheet Formulation g w/w % Zn 3375 81.70% KMnO₄ 1.9 0.04% Carbon 268.1 6.49% polytetrafluoroethylene 486 11.76% Total 4131.0 100.0%

The properties of the produced composite heaters are shown in table 2. The dry porosity is determined by calculating the theoretical density of the components in the dry heater sheet and then subtracting the apparent density from the theoretical density. The difference is then divided by the theoretical density to determine the dry porosity.

TABLE 2 Apparent Sheet Weight, Thickness Thickness Vol- Density Dry % Properties g (inches) (cm) ume g/cm3 Porosity Max 30.34 0.050 0.127 15.77 2.00 64.3% Min 28.20 0.048 0.122 15.14 1.79 60.0% Average 29.13 0.049 0.124 15.43 1.89 62.3%

The composite heaters were activated with various amounts of a 20% (by weight) potassium chloride solution and assembled into pouches. The different amounts of the electrolyte solution are shown in Table 3. The use of the various amounts also resulted in different wet porosities, also shown in Table 3. The wet porosity is determined by calculating the free volume in the dry heater sheet, subtracting the volume of activator solution added to the sheet to determine the final free volume and then dividing by the sheet volume.

TABLE 3 Free Total Vol- Activator Liquid Final Free Final % ume, Solution Volume, Volume, Wet Porosity cm³ Weight, g cm³ cm³ Porosity Group A 61.9% 9.37 4.9 4.3 5.09 33.6% Group B 61.9% 9.37 6.4 5.5 3.83 25.3% Group 60.9% 9.23 8.0 7.0 2.27 15.0% C(a) Group 63.6% 10.03 7.8 6.7 3.29 20.8% C(b) Group D 63.6% 10.03 9.2 8.0 2.02 12.8% Group E 62.8% 9.90 10.88 9.46 0.44 2.8%

The performance of each of the composite heaters was evaluated in a standard eight ounce water bag test in which the temperature of water is monitored during the heating process.

The parameters of the test that were measured are as follows: the temperature rise in five minutes; the time to raise the water temperature by 100° F. from an initial temperature of 40° F.; the time to reach the maximum temperature; and, the maximum temperature achieved. In these tests, the 140° F. desired temperature was chosen as a desired temperature because a temperature of 140° F. is a desired temperature for a comestible when heated from a cold temperature. As used herein “desired temperature” means a temperature that is chosen and which represents a temperature sufficient to achieve the purposes of the heater (i.e., heat a comestible, boil water, melt ice, etc.).

FIGS. 1-3 illustrate the effect of wet porosity on the performance of heater pouches.

More specifically, FIG. 1 shows the temperature rise in five minutes for various composite heaters. As shown and demonstrated by FIG. 1, the lower the porosity, the slower the temperature rise (in the initial five minutes). This indicates a lack of oxygen access to reaction sites within the composite heater. By increasing the wet porosity, it is believed there is more access to the reaction sites within the heater structure leading to a faster rate of reaction and higher temperature at five minutes.

The effect of wet porosity on the time that it takes for a heater pouch to achieve a 100° F. temperature rise in an eight ounce water bag test is shown in FIG. 2. As shown, in the range of 15-35% wet porosity there is only a small impact on the time to 100° F. rise. However, lowering the wet porosity to less than 10% greatly increases the time needed to achieve the same temperature rise. This effect is believed to also indicate a reduced oxygen access to reaction sites leading to a slower reaction rate and thus, a longer time for the temperature rise. As a result, it is believed that more than approximately 12 minutes to reach the desired temperature was unacceptable. An “acceptable time” would be a time in which the heater reaches the desired temperature (and thus can sufficiently perform its desired function).

Finally, the effect of wet porosity on the time it takes to reach the maximum water temperature in the test is shown in FIG. 3. As is demonstrated in FIG. 3, the time to maximum increases as the wet porosity decreases. This trend is believed to reflect the lower access to reaction sites due to a decrease in available porosity in the heater sheet.

As shown in FIG. 4, heater 6 may be disposed inside of package 5. Such package 5 may be a pouch comprising first sheet 9 and second sheet 12. Second sheet 12 includes a plurality of openings 14 forming oxygen access portion 11. Disposed over at least oxygen access portion 11 may be flap 8 (or other similar structure capable of selectively opening and preferably re-closing). Flap 8 may include adhesive 10 to secure flap 8 over oxygen access portion 11 when the production of heat is not desired or no longer desired. As shown, package 5 may include side 7 without any openings 14; however, the depicted package is merely a representative package which selectively prevents oxygen access to heater 6 to control an exothermic reaction between heater 6 and atmospheric oxygen.

Heater 6 is made according to the present invention, and as disclosed above, is a porous flexible substrate which includes a reducing agent, a binder, and a promoter. Heater 6 is also activated with an electrolyte solution. Furthermore, heater 6 has a wet porosity of between approximately 15-35%.

Such a heater will provide a sufficient amount of heat and reach the desired temperature within an acceptable amount of time, based in part, upon the porosity of the heater itself.

It is to be understood that additional embodiments of the present invention described herein may be contemplated by one of ordinary skill in the art and that the scope of the present invention is not limited to the embodiments disclosed. While specific embodiments of the present invention have been illustrated and described, numerous modifications come to mind without significantly departing from the spirit of the invention, and the scope of protection is only limited by the scope of the accompanying claims. 

What is claimed is:
 1. A heater comprising: a composite heater substrate that exothermically reacts with oxygen, wherein the composite heater substrate has a wet porosity of between 15-35%.
 2. The heater of claim 1 wherein the composite heater substrate has a dry porosity of approximately 60%.
 3. The heater of claim 1 wherein the composite heater substrate has a dry porosity of approximately between 60-65%.
 4. The heater of claim 1 wherein the heater comprises: a reducing agent, a binder, a promoter and an electrolyte.
 5. A heater comprising: a porous flexible substrate including a reducing agent, a binder, and a promoter, the porous flexible substrate being activated with an electrolyte solution; and, a package surrounding the porous flexible substrate to selectively prevent oxygen access to the porous flexible substrate to control an exothermic reaction between the porous flexible substrate and atmospheric oxygen, wherein the porous flexible substrate has a wet porosity of between approximately 15-35%.
 6. The heater of claim 5 wherein the porous flexible substrate has a dry porosity of approximately 60%.
 7. The heater of claim 5 wherein the porous flexible substrate has a dry porosity of approximately between 60-65%.
 8. The heater of claim 5, wherein the heater includes approximately 82% by weight of the reducing agent, approximately 6.5% by weight of promoter, and approximately 12% of binder.
 9. The heater of claim 8, wherein the heater has a dry porosity of approximately 60%.
 10. The heater of claim 9, wherein the heater includes between approximately 5-8 g of electrolyte solution.
 11. The heater of claim 10, wherein the electrolyte solution is a 20% by weight solution of potassium chloride.
 12. A heater comprising: a flexible substrate that includes a binder and a reducing agent that will produce heat in the present of oxygen; the flexible substrate being porous; the flexible substrate being activated by an electrolyte solution such that the flexible substrate includes a wet porosity sufficient to achieve a desired temperature in an acceptable amount of time.
 13. The heater of claim 12, wherein the desired temperature is 140° F.
 14. The heater of claim 13, wherein the acceptable amount of time is less than 15 minutes.
 15. The heater of claim 12, wherein the wet porosity is between approximately 15-35%.
 16. The heater of claim 12, wherein the desired temperature is approximately 100° F. than an initial temperature of the heater. 